This invention relates generally to an internal combustion engine and, more particularly, to a valve guide assembly for an internal combustion engine. Present internal combustion engines are being manufactured for increased efficiency and greater horsepower outputs. In order to achieve greater efficiency, exhaust temperatures are increased as less heat is transferred to the cooling system. The increased exhaust temperatures increase the output of any exhaust energy recovery hardware, such as the turbocharger, and subsequently, the performance of the engine.
In conventional engines, engine valve guides have been made from an iron based material. However, these iron based valve guides are not suitable for operating within the high exhaust temperature ranges reached with high efficiency engines. Therefore, to overcome this problem the valve guides for high efficiency engines are typically made from a ceramic material.
An example of a valve guide composed of a ceramic material is disclosed in U.S. Pat. No. 4,688,527 issued to Donald H. Mott, et al. on Aug. 25, 1987. In order to support and sealingly interact with a conventional engine poppet-type valve it is necessary that the valve guide have a through bore for receiving a stem of a valve. In addition, it is typically required that the entire length of the through bore be machined in order to obtain the proper dimensions and surface finish. Many of these high efficiency engines require valve guide assemblies that are quite long, on the order of 92 to 170 millimeters in length. Such long valve guide assemblies require long quills and small diameter grinding wheels to form the through bore and create the proper surface finish. Such long quills are easily distorted when a load is placed on them and therefore, the forces during grinding must be kept low in order to prevent such distortion. In addition, such long quills limit the surface feed rates. The low grinding forces and surface feed rates significantly increase the amount of time required to finish the interior surface of the through bore, thus increasing significantly the cost. The present invention is directed to overcoming the problems set forth above.